The invention relates to harvesting equipment, and more specifically to a control valve for activating a hydraulic piston-cylinder unit thereby driving a cutter bar in an oscillatory manner.
German Patent DE 195 29 067.4 illustrates a harvesting machine having a frontal attachment used for harvesting crops. The harvesting machine has a driving element containing a frame and an oscillating cutter bar, and a conveying element containing a rotary reel and an intake auger for conveying the harvested crop. Cutter blades are used in the oscillating cutter bar of the harvesting machines to cut crop during harvesting. Relevant working devices and a gear box are located externally from the cutter bar. The gear box and the drive means are extremely powerfull, especially for driving larger cutter bars, so as to ensure that the cutter blades are at the correct cutting position over a full working width of the cutter bars. The gear box and the drive means must also be able to withstand very large oscillatory forces. Due to the large length of the cutter bars and the power required to move the cutter blades, there are large inertial forces being produced by the cutter bar as it oscillates. These forces must be taken into account when designing the structure of the cutter bar. In addition, the force flow-path from the drive source to the cutter blades is very extensive and complex. The conventional mechanical drives used for driving the cutter blades of the cutter bar are of heavy and complex linking constructions which is a disadvantage.
German Design Patent 8209146.3 obviates this disadvantage by means of a hydraulic piston-cylinder unit for driving the cutter blades. This design generally functions satisfactorily. A switch-over valve constantly reverses the hydraulic fluid stream to the piston-cylinder unit. This switch-over valve is a critical feature and is actuated hydraulically. However, the disadvantage of this type of system is that it presupposes that there will always be a sufficient quantity of and pressure from hydraulic fluid for switching the switch-over valve into its respective end positions and retaining it there. If, for example, the pressure falls when the switch-over valve is in an intermediary position, it is virtually impossible to reset the system for continuous operation without manual intervention.
The present invention is directed to overcoming one or more of the problems set forth above.
An aspect of the invention is to provide a harvester with an improved mechanically actuated directional control valve for insuring that a valve piston of the mechanically actuated directional control valve reaches either a first or second end position even under a sudden decrease in pressure.
Another aspect of this invention is to provide a harvester having a hydraulic piston-cylinder unit operatively connected to a mechanically actuate directional control valve and a cutter bar. The harvester includes a valve housing located in the mechanically actuate directional control valve, a valve piston axially displaceable and operatively, moveably mounted in a central boring in the mechanically actuate directional control valve for switching the hydraulic piston-cylinder unit thereby driving a cutter bar in an oscillatory manner, and a first plunger and a second plunger operatively, alternatively, and axially displaced in the valve piston in the mechanically actuate directional control valve, wherein the mechanically actuate directional control valve is operatively connected to the hydraulic piston-cylinder unit.
The above aspects are merely illustrative examples of a few of the innumerable aspects associated with the present invention and should not be deemed an all-inclusive listing in any manner whatsoever.